= arrhyth fr distal to His bundle
-Nonsustained VT = <30sec long, no HD xx
-Sustained VT = >30sec long
-Incessant VT = ongoing, often in ASx infant
-Slow VT <150bpm
-Monomorphic vs Polymorphic VT
( w PVCs describe them as Uniform or Multiform)
-Bidirectional VT- a form whereby the QRS axis changes across the baseline
-Polymorphic more likely to --> VF
-may be provoked or suppressed by exertion
-Mechanisms
-Reentry
-in hrt w scar, eg post-op, post MI fr cor dz, or abNl cor Q,
-most are via the myocardium, but some may use a bundle branch or Purkinje system
-Automaticity
-more likely in a structurally Nl heart, maybe w stretch on the hrt
-Triggered Automaticity
-Some may be suppressed w adenosine, b-blocker, CCB
-Some mediated by cyclic-AMP; some provoked by catecholamines
-Some may be assoc w a repol abNly- Long QT, Brugada...
Sx
-may be ASx
-may feel irreg heart beat, or racing heart sensation,
-Accelerated idioventricular rhythm- =ASx BT, benign, not >120bpm
-if >120bpm and sustained, may --> tachy mediated CM
-if pt p/w CM + VT, unsure which caused which, and affects mgt decision- if DCM w 2y VT, c/s AICD, if VT w 2y CM, c/s Rx for VT bc pt may improve the hrt failure...
-Syncope & sudden death - least common presentation
-uncommon unless infiltrative or hypertrophied heart, or h/o CHD surg or ch hrt dysfx xx...
ECG
-QRS wider than Nl for age (but in infant may still be <80msec)
-see both an initial and terminal conduction delay, harder to see at faster rates and in younger kids
-see AV dissociation (but may be hard to see if P buried in QRS)
-may see VA association, espec in younger pt w a healthy AV Nd- give adenosine to DDx (will stop the tachy if it is AV Nd dependent SVT, will stop only P waves if VT w retro condudction) BUT dont give adenosine if it is irregular rhythym- might be WPW
-see fusion & capture beats (less likely to see if higher VT rate)
-check QRS vector planes to determine likely site of origin
DDx of wide complex tachy
-sinus/atrial tachy w preexcitation or w a pre-existing BBB
-orthodromic AV reentry tachy w BB aberrancy
-antidromic AV reentry w a typical or atypical (Mahaim) AP
-AVNRT w BB aberrancy or bystander ventric preexcitation
-A-fib in WPW pt can look like VT but it is irregularly irreg, and morph of QRS is very irreg too.
Clinical Investigation
-paroxysmal or chronic?
-dizzy?, chest Sx/discomfort?, dyspnea, weakness, HA?
-CHD? AHD?
-substance abuse? toxin exposure? viral exposure?
-FHx- syncope, sz, sudden cardiac death, familial arrhyth?
-PE
-weak pulses, cannon a waves at neck, diastolic filling sounds bc of underlying CM
-c/s electrolytes, signs of inflmn, thydroid xx
-Echo- CHD, AHD, ti=umors, RVdysplasia w fatty replacement or abNl hypertrophy, ...
-MRI- fatty replacement w arrhythmogenic RV dysplasia, focal myocardial dz
-Exercise stress test- treadmill- limited use except to Dx/check effect of Tx on exercise provoked VT
-same w Holter
-EP Study
-only if you might Tx
-c/s if high density PVCs which may trigger a VT, or if +Sx and poss tachyarrhythmia...
-or to unmask a life threatening inducible sustained VT, or to check Tx effectiveness...
Tx
-if HD xx
-direct current cardioversion
-no HD xx
-c/s adenosine trial
-if VT is fr post inf aspect of LV septum, and look like RBBB and superior axis morph--> c/s CCB w slow IV push of verapamil
-in infants w this, first give slow IV push of Ca at Nl replacement dose to avoid lowering BP w verapamil (in case the latter is given too quickly)
-c/s Procainamide slow push /20min 10-15mg/kg/dose - will Tx VT & other tachyarrhtyhmias too
-c/s IV amiodarone
-once pt back in sinus, then give ch Tx:
-Tx underlying structural problems (e.g. replace bad PVlv in TOF pt...)
-ok just to watch if ASx/minimal Sx w/o other hrt dz, likely to resolve
-b-blocker if no hrt dz, and modestly Sx exercise provoked monomorphic VT fr RVOT or LVOT
-CCB- Verapamil- PO, well tolerated for Ca Sn left VT
-Digoxin - no direct role in VT Tx, but may indirecttly improve fx
-Type IA & IB (Proc, Quinidine, Disopyramide, diphenylhantoin, tocainide) - less used bc xx
-only use if RF ablation ng for this pt
-Type IC- effective for SVT in young pts, and maybe also for VT
-the pro-arrhythmia occurs soon after initiation, so start in house on monitor
-be careful if cardiac dysfx, espec postop
-Type III- very effective for VT_ Sotalol- has a b blockade effect in addition to Type III effect
-Amio effective but long term xxx must be considered
-Surgery
-RF/cryoablation in EP lab
-Indication- best if structurally Nl hrt & focal VT origin
-Sx sustained or repetitive non-sustained VT, exercise provokable VT fr RVOT despite bblocker, and Ca Sn LV septal VT despite CCBs.
-Also c/s if pt has arrhythmogenic RV dysplasia- but more likely to be multifocal & ablating at fatty sites is more risky
-if pt has structural hrt dz/is post op, then VT more likely to be reentry in nature; while it is possible to ablate a pathway if it is a single reentry w regular borders, it is much harder w a more complex reentry circuit/many borders
-ICD- often now not need thoracotomy